The invention relates to improvements in power trains for motor vehicles, and more particularly to improvements in power trains which employ automated transmissions and/or automated torque transmission systems (such as friction clutches). Still more particularly, the invention relates to improvements in power trains which employ sensors and which can be operated in a novel and improved way in the event of a temporary or non-reversible failure of one or more sensors. The invention also relates to improvements in methods of operating power trains of the above outlined character.
It is known to provide a motor vehicle (such as a passenger car or a truck) with a power train wherein an automated clutch determines the magnitude of the torque being transmitted from the rotary output element of a prime mover (such as a camshaft or the crankshaft of an internal combustion engine) to a rotary input element of a variable speed transmission. The condition of the clutch (i.e., the extent of its engagement or disengagement) is determined by signals furnished by a control unit to one or more actuators (such as electric, fluid-operated or other suitable motors) which actually select the condition of the clutch, and a signal processing circuit of the control unit receives and processes signals from several sensors (such as RPM monitoring devices, sensors responding to changes in the condition of one or more brakes, one or more sensors which monitor the selected gear of the transmission, one or more sensors serving to monitor the positions of the gas pedal and/or the throttle valve for the engine, and/or others. The arrangement is normally such that the motor vehicle is set in motion (e.g., to carry out a crawling or creeping movement) when the combustion engine is on, the transmission is in (forward or reverse) gear, and the gas pedal is not depressed. Such mode of operation of the control system including the control unit and the actuator(s) for the clutch can be defined as a normal or standard operating mode.
Control units of the just outlined character can be utilized in power trains with automated transmissions and/or automated clutches. The clutch is normally installed in the power train in such a way that it can transmit torque between the prime mover and the driven wheels of the vehicle, particularly between the engine and the transmission. The vehicle can be caused to perform a desired creeping or crawling movement in response to appropriate adjustments of the clutch, i.e., in response to appropriate selection of the torque which the clutch can transmit (e.g., from the engine to the transmission of the vehicle). A creeping or crawling movement is often desirable when the engine is on, the transmission is shifted into a selected (forward or reverse) gear, the brake(s) is (or are) not applied, and the gas pedal is not depressed. The speed of creeping movement is reduced, or such movement is interrupted or terminated, when the operator of the motor vehicle decides to apply a brake (e.g., the standard vehicle brake which is controlled by a brake pedal and/or a parking brake which is actuated by a reciprocable and/or pivotable manually operated lever). Reference may be had, for example, to published German patent application Serial No. 44 26 260.
The sensors which generate and transmit signals denoting one or more parameters (such as the RPM of a rotary element of the combustion engine, the RPM of a rotary input or output element of the transmission, the extent of engagement (i.e., the condition) of the friction clutch, the position (extent of depression) of the gas pedal, the inclination of a pivotable component (such as a flap) of the throttle valve, the position(s) of the brake actuating member(s) and/or others) can be connected with the corresponding inputs of the (normally electronic) circuitry of the control unit by electrical conductors, by one or more data buses (such as CAN buses) or in any other suitable way. Such signals can also be transmitted to the inputs of an electronic engine circuit, to the inputs of an antiblock system (ABS) and/or to the signal storing and/or processing circuits. Furthermore, the various circuits (such as the electronic circuit of the control unit for an automatic or automated clutch and/or automatic or automated transmission and the electronic circuit for the internal combustion engine) can be connected to each other by buses and/or other types of signal transmitting conductors.
A drawback of presently known controls for the components of power trains in motor vehicles is that they are not capable of reacting, or reacting satisfactorily, to the development of malfunctions, such as the temporary or uninterrupted (permanent) malfunctioning of one or more sensors and/or their connections with the signal-receiving circuit or circuits. For example, the component parts of a control system can develop short circuits, their conductors (such as cables) are likely to break as a result of an excessive impact or due to age, or the signals being transmitted by the sensors can become unreliable for other reasons. This can result in an interruption of the path or paths for the transmission of important or vital information pertaining to the condition of the motor vehicle and its power train. For example, a malfunctioning can involve a short-lasting or continuous interruption of the transmission of signals from a sensor for the gas pedal to the control circuit for an automated clutch, or an interruption of the transmission of signals to such control circuit from the sensor or sensors which monitors or monitor the condition (such as the selected gear or the momentarily effective gear) of the transmission. Such interruption is or can be attributable to a defect or to the defects of one or more sensors and/or to the defect of a connection between a sensor and a signal processing circuit.
It is already known to construct a control circuit in such a way that it automatically shifts from a normal or standard operating mode to an emergency or standby mode in response to receipt of information denoting that one or more sensors and/or the connection(s) between one or more sensors and the control unit is or are defective. As a rule, the operation of a control circuit in accordance with an emergency or standby mode (hereinafter called emergency mode) involves an undesirable (often very pronounced) reduction of comfort to the operator and/or other occupant(s) of the affected motor vehicle. Alternatively, or in addition to a reduction of comfort, the operation in accordance with an emergency mode often entails a pronounced reduction of the versatility (such as maneuvrability) of the affected motor vehicle.
If the sensors are not defective and the conections between the sensors and one or more control circuits are also satisfactory, the operator of the motor vehicle can shift the transmission into a selected gear while the engine is running, while the brake or brakes is or are not activated, and while the gas pedal is not depressed; this causes the vehicle to creep or crawl at a selected speed. Such speed is reduced to zero in response to shifting of the transmission from a forward gear or from the rearward gear into neutral.
If the operation of the control unit in accordance with an emergency mode is attributable to the defect(s) of one or more sensors which monitor the selected gear of the transmission and/or the defects of the signal transmitting connection(s) between such sensor(s) and the control unit, the latter cannot ascertain the condition (such as the selected gear) of the transmission while the engine is running, while the transmission is in a forward gear or in reverse gear, and while the gas pedal is not depressed. If the operator of the motor vehicle interprets such emergency mode as denoting that the transmission is shifted into a forward gear or into the reverse gear while the transmission is actually in neutral (or vice versa), this can result in an unwarranted, undesirable or dangerous crawling or creeping movement of the motor vehicle while the vehicle should remain or or should come to a standstill. If the operator misinterprets the actual condition of the transmission and/or of the clutch, the vehicle is likely to carry out an abrupt forward or rearward movement in response to subsequent shifting of the transmission into reverse or into a forward gear. In other words, the operation of the control unit or units in accordance with a conventional emergency procedure or mode is not satisfactory and is likely to involve a serious danger as well as serious discomfort to the occupant or occupants of the vehicle.